How is the activity of shikimate dehydrogenase from the root of Petroselinum crispum (parsley) regulated and which side reactions are catalyzed?

Inhibitors of the shikimate pathway are widely used as herbicides, antibiotics, and anti-infectious drugs. However, the regulation of the shikimic pathway is complex, and little is known about the feedback regulation of the shikimate dehydrogenase (SDH, EC 1.1.1.25) in plants. Thus, the aim of this study was to elucidate the kinetic mechanism of SDH purified from the root of Petroselinum crispum (parsley), to determine all possible reaction products and to identify phenylpropanoid compounds that affect its activity. Our results showed that the bisubstrate reaction catalyzed by P. crispum SDH follows a sequential ordered mechanism, except for three dead-end complexes. The main and lateral reactions of SDH were monitored by mass spectrometry, thereby detecting protocatechuic acid as a byproduct. Gallic acid was formed non-enzymatically, whereas quinate was not detected. Several polyphenolic compounds inhibited SDH activity, especially tannic, caffeic and chlorogenic acids, with IC₅₀ 0.014 mM, 0.15 mM, and 0.19 mM, respectively. The number of hydroxyl groups influenced their inhibition effect on SDH, and p-coumaric, t-ferulic, sinapic, syringic and salicylic acids were less effective SDH inhibitors. Nevertheless, one branch of the phenylpropanoid pathway may affect SDH activity through feedback regulation.

Shikimic acid: review of its analytical, isolation, and purification techniques from plant and microbial sources

Shikimic acid properties and its available analytical techniques are discussed. Plants having the highest content of shikimic acid are shown. The existing isolation methods are analyzed and the most optimal approaches to extracting this acid from natural sources (plants and microorganisms) are considered.